A phase change material may be used in a memory cell to store a bit of data. Phase change materials that are used in memory devices may exhibit at least two different states. These states may be referred to as the amorphous and crystalline states. These states may be distinguished because the amorphous state generally exhibits higher resistivity than the crystalline state. Generally, the amorphous state involves a more disordered atomic structure.
Rectangular current pulses may be used to program the phase change material to a desired state. The amplitude of the current pulse may be varied to change the resistance of the phase change material. However, variations in the materials, fabrication processes, and operating environment may cause the resulting resistance in different memory cells of a memory array to vary for a given rectangular current pulse. Thus, when programming multiple memory cells in a memory array, due to these variations, some cells may be programmed to one state, while others may be programmed to a different state when the same rectangular pulse is applied to each memory cell, or some cells while programmed to the desired state may not have adequate sense margins.
Thus, there is a continuing need for better ways to program memory cells in memory systems using phase change materials.